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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - gep(ptr, undef) isn't undef"
href="https://bugs.llvm.org/show_bug.cgi?id=45445">45445</a>
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<th>Summary</th>
<td>gep(ptr, undef) isn't undef
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Keywords</th>
<td>miscompilation
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nunoplopes@sapo.pt
</td>
</tr>
<tr>
<th>CC</th>
<td>efriedma@quicinc.com, juneyoung.lee@sf.snu.ac.kr, lebedev.ri@gmail.com, llvm-bugs@lists.llvm.org, regehr@cs.utah.edu, spatel+llvm@rotateright.com
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<pre>Test: Transforms/InstCombine/vec_demanded_elts.ll
Summary: gep(ptr, undef) isn't undef. It's a pointer based on ptr with an undef
offset (a multiple of 4 in this case). A way to make this correct is to return
<%base, %base>.
define <2 x *> @gep_all_lanes_undef(* %base, i64 %idx) {
%basevec = insertelement <2 x *> undef, * %base, i32 0
%idxvec = insertelement <2 x i64> undef, i64 %idx, i32 1
%gep = gep <2 x *> %basevec, 4 x <2 x i64> %idxvec
ret <2 x *> %gep
}
=>
define <2 x *> @gep_all_lanes_undef(* %base, i64 %idx) {
ret <2 x *> undef
}
Transformation doesn't verify!
ERROR: Value mismatch
Example:
* %base = pointer(non-local, block_id=1, offset=0)
i64 %idx = #x0000000000080000 (524288)
Source:
<2 x *> %basevec = < pointer(non-local, block_id=1, offset=0), null >
<2 x i64> %idxvec = < undef, #x0000000000080000 (524288) >
<2 x *> %gep = < pointer(non-local, block_id=1, offset=0), pointer(non-local,
block_id=0, offset=2097152) >
Target:
Source value: < pointer(non-local, block_id=1, offset=0), pointer(non-local,
block_id=0, offset=2097152) >
Target value: < pointer(non-local, block_id=0, offset=16), null >
<a href="https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=2009353267698970&test=Transforms%2FInstCombine%2Fvec_demanded_elts.ll">https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=2009353267698970&test=Transforms%2FInstCombine%2Fvec_demanded_elts.ll</a></pre>
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